Brake condition monitoring

ABSTRACT

A system and method for monitoring the applications of carbon-carbon brakes of an aircraft to determine brake condition and operate a brake maintenance program or charge a brake system user. The system and method includes monitoring each actuation of the brakes and making a separate record of each actuation of the brakes in which there is relative movement of the facing friction surfaces that cause wear, and from that separate record determining brake usage. The monitoring may include measuring changes and processing the signals to distinguish between those which fall below and those which are above a threshold value. The method and system may comprise sensing a plurality of braking parameters having values dependent upon the wear in the system and different faults of the system, and identifying and recording wear and faults based on combinations of values of the parameters.

BACKGROUND OF INVENTION

This invention relates to a system and method for monitoring brakeapplications, more particularly but not exclusively monitoring theapplication of the brakes of an aircraft, for example, to determine thecondition of the brakes. The invention also relates to a system foroperating a braking system maintenance program and to a system forcharging a user of a braking system.

Carbon-carbon brake discs are commonly used in aircraft brakes. Theservice life of a carbon-carbon brake is commonly quoted in terms of thenumber of landings the brake discs are expected to achieve beforereplacement, the number of landings being routinely logged formaintenance and airworthiness requirements. The expected number oflandings is commonly used as a guarantee of minimum service life forheat packs that are sold or to calculate the cost per brake landing(CBL) where brake heat packs are leased to operators by the brakemanufacturers.

Aircraft brakes, especially those employing carbon-carbon compositematerials as the friction discs in a multi-disc arrangement, may sufferdamage that can affect the performance of the brake during service.Routine inspection of brakes between scheduled services includesinspecting the wear pin to ensure sufficient material is available toenable the heat pack to safely absorb the energy of a stop withoutoverheating and damage to the heat pack and surrounding components.Inspection of the wear pin will only reveal when the heat pack isreaching the end of its wear life and will not show other problems thatcan adversely affect performance of the brake such as broken discs,missing drive tenons, oxidation, uneven disc wear, brake drag orcontamination.

It is desirable to have accurate information for determining thecondition and predicting the life of carbon-carbon brake discs. This isimportant for safety as well as commercial reasons. For example, thehigh cost of carbon-carbon brake discs and delivery lead times in theorder of six months makes provisioning of spares an important issue ifinventory and hence working capital is to be minimized.

In use aircraft brakes are applied in five situations: when landing,when taxiing, when stationary, during pre-retract braking and, veryrarely, during a rejected take off. This is an important point, forexample, because it has been realized that the rate of wear of a carbonbrake is dependent to a major extent on the number of brake operationseffected and not on the energy dissipated during the operation. Thus,the wear during a taxi snub on a cold carbon-carbon brake is similar tothat of a full landing.

The prior art relating to brake monitoring includes DE-A-3433236 whichdiscloses a brake application monitoring device intended for use invehicle or aircraft. This device comprises a chart recorder with tracesdriven by a transducer measuring the brake force, e.g. by sensing thehydraulic pressure applied, and an intertial sensor responsive to theactual deceleration of the vehicle or aircraft. However, there areseveral disadvantages with this proposal. For example, the brakes on anaircraft may require an applied pressure of approximately 150 psi (10bar) simply to close the clearance in the brake before any brakingeffect is seen. However, a relatively small increase in that appliedpressure may be all that is necessary to achieve the desired brakingeffect for a taxi snub. In many existing systems there is little or nosensing of brake pressure which means that modifications to thosesystems would be needed if brake pressure is to be used as a means ofdetermining brake application. The use of an inertial sensor is not ableto identify all kinds of braking operation carried out, for examplecheck braking against engine thrust, and it might erroneously identifyas a braking application a deceleration due to drag, wind effects orthrottling back the engines as a braking application.

In the context of a braking system such as an aircraft wheel brake, itis known to measure physical parameters associated with the brakingeffect during an operation of the system with a view to regulating thateffect.

For example, in a hydraulic servo operated aircraft brake system(autobrake) the extent to which the pilot has depressed the brake pedal,i.e. the brake demand, may be measured and the resulting hydraulicpressure applied to the brakes regulated to a value appropriate to thedemand. In more complex examples, further parameters are measured. Thus,U.S. Pat. No. 4,790,606 to Reinecke discloses apparatus for measuringand/or regulating a braking force, which apparatus includes adeceleration sensor, a brake temperature sensor, a mass sensor and anevaluation means which uses the signals from these sensors to achievethe measurement and/or regulation. U.S. Pat. No. 4,592,213 to Rapoportdiscloses a braking system comprising temperature, friction and pressuresensors and means for comparing the signals from these sensors withpredetermined values and automatically operating the braking systemaccordingly. U.S. Pat. No. 4,572,585 to Guichard and U.S. Pat. No.4,043,607 to Signorelli et al also disclose systems of such a nature.

In some cases, the existence of excessively inefficient braking issignaled, e.g. by a warning signal to the pilot of an aircraft.

SUMMARY OF THE INVENTION

According to the invention there is provided a brake conditionmonitoring system and method in accordance with the claims.

The invention could be applied to an existing or new aircraft by theaddition to the brake of a stand-alone unit with its own power supply oran external power supply from the aircraft systems. Alternatively, brakecontrol hardware and/or software could be modified to incorporate thesystem into existing and new aircraft.

Methods for data storage and downloading such stored information arewell known. The information on brake usage could be downloaded at someconvenient time such as during maintenance of the aircraft. Data couldbe read directly from a visual display or downloaded to a portablefacility for analysis later. Alternatively the recording unit could beremoved for analysis at another site. The information could also bestored, for example, on a memory card that would be easier to removethan the whole unit.

The system of the invention could utilize the current anti-skid controlunit (ASCU) by including extra algorithms within the current software,or a stand-alone box that could be positioned either on the brake orsomewhere within the aircraft. Different parameters (hydraulic pressure,temperature, wheel speed, torque, pedal deflection, brake wear) could beused within algorithms to detect when an application has taken place andpossibly what kind of application it was. The recorded information couldbe downloaded for analysis of the brake usage and the information couldbe used for maintenance, spares provisioning and/or charging purposes.

Information downloaded from the system could be used to build a detailedpicture over a period of time of brake usage for each airline operatingan aircraft type. This information could then be used to accuratelypredict when maintenance will be required and when heat packs will needchanging. This will allow more accurate provisioning of heat packspares, reducing inventory of these expensive carbon discs at theairline and brake manufacturer and hence reducing operating costs.

Information downloaded from the system could be used to give morereliable guarantees of brake service life by accounting for the wear dueto different types of brake usage. The information could alternativelybe used to extend a CBL payment scheme to charge for all brakeapplications, rather than only landings, with the charge for each brakeapplication related to the type of usage and associated wear.

The monitoring system could be an additional unit added to the aircraftor it could be incorporated into the existing brake management controlsystem.

Congestion at many airports results in a considerable number of brakeapplications during taxiing where relatively little energy is dissipatedcompared with that dissipated during a landing run. This high number ofbrake applications during taxi braking can considerably reduce theexpected life of the carbon brake disc heat pack. This can result inadditional cost for aircraft operators where expected brake life is notachieved. Where operators pay for brakes on a CBL basis, an airline thataverages only two taxi snubs per landing sequence would be charged thesame CBL rate as an airline that operated from busier airports andaveraged 20 snubs per sequence. If information on the type of brakeapplication could be recorded a more detailed picture of an aircraft'sbrake usage could be built up to assist stock control and develop apricing scheme reflecting brake usage. A knowledge of the factorsinfluencing brake life could also be used by airlines to educate pilotsin brake techniques to extend brake life and reduce operating costs.

When the aircraft is stationary there is no relative rotational movementof contacting friction surfaces and, as applications of the brakes willnot generate wear of the carbon, it may be decided that it is notdesirable to record these applications. The difference betweenapplications of the brakes while stationary and applications where theaircraft is moving can be ascertained by a system that considers theaircraft speed at the moment the brake is applied to considers theconversion of kinetic energy to heat. If the aircraft speed, measuredfor example by the signal from a wheel speed transducer, is below acertain threshold value the aircraft can be considered to be stationaryand the brake application will not be logged/recorded. If the aircraftspeed is equal to or above the threshold value the application of thebrake will be recorded to provide information on brake usage.

During a brake application the braking energy is dissipated through thebrake as heat. Therefore, it is theoretically possible to sense even theslightest brake application through the change in brake temperature.Temperature sensors are routinely incorporated in brake units so it ispossible to sense brake applications within the system with no orlimited modification to existing brakes. The brake temperature signalcan be processed to give reliable indications of all brake applications.

As noted, aircraft brakes may be applied in five different situations;when landing, when taxiing, when stationary, during pre-retract brakingand, occasionally, during a rejected take-off. Each type of brakeapplication is carried out within a respective range of inputs, forexample brake fluid pressure, pilot pedal deflection or wheel speed andeach type of brake application should produce a relatively predictableresponse from the brake in terms of outputs such as, for example, heatpack temperature rise or torque generated.

The brake demand inputs are monitored and processed to predict expectedbrake outputs. The actual outputs are also monitored and compared withthe expected or predicted outputs to derive information on the conditionof the brake. Such information could be used to predict service life ordetect problems that might lead to unscheduled maintenance or prematurebrake heat pack removal.

Preferably the system will predict the expected brake outputs from themeasured inputs and compare such expected outputs with the measuredoutputs. Where there is a variation between expected and measuredoutputs the system will determine whether the variation is the result ofa defect in the condition of the brake actuator or brake heat pack.

Such a system for monitoring the condition of the brakes could becarried out within the brake control system, with the addition ofhardware or software as necessary. Alternatively, monitoring could becarried out within a dedicated condition-monitoring unit fitted to theaircraft and receiving signals from brake control system hardwarecomponents and additional hardware components if required.

The system can include means to alert the pilot or ground personnel if afault in the brake condition is detected to allow maintenance to becarried out at the earliest opportunity so as to minimize the risks toaircraft safety and increase aircraft dispatchability. For alerting thepilot to any fault a display could be provided in the cockpit. Personnelon the ground could be alerted to any detected faults by a display on orfrom the brake control system or dedicated condition monitoring systemduring pre-flight checks or by a signal to a ground base.

Signals that could be monitored and processed to provide a brake“signature” from which information on brake condition can be derivedinclude but are not limited to pilot pedal deflection, brake fluidpressure, wheel speed, anti-skid activity, brake temperature, braketorque, brake wear, number of brake applications, brake applicationtime, vibration, brake chassis acceleration, acoustic signature, brakeodor. In addition, information can be received from other aircraftsystems such as, for example, aircraft weight. Some of these signals canbe regarded as inputs to the brake and reflect the type of brakeapplication that is called for by the pilot or auto-brake system, forexample a landing or taxi snub. Such inputs include but are not limitedto pilot pedal deflection or auto brake demand, brake fluid pressure,brake application time and wheel speed. Other monitored signals can beregarded as outputs resulting from the brake application and conditionof the brake. Such outputs include but are not limited to brake torque,brake temperature, vibration, acoustic signature, acceleration and brakeodor.

Where a brake heat pack is in as new condition with full amount ofwearable material available and all disc drive tenons in place the heatpack will have a maximum number of friction surfaces in operation duringbrake applications. In addition there will be a maximum heat pack massavailable to absorb the heat generated during the brake application.From the processing of a combination of some or all measured inputsincluding but not limited to wheel speed, pilot brake pedal orauto-brake demand, brake fluid pressure and anti-skid activity a numberof expected outputs can be determined. Such outputs or brake signatureinclude but are not limited to brake torque, brake temperature, acousticsignal, vibration, acceleration and brake odor.

As the condition of the heat pack changes the monitored output orsignature described above will change for any given set of brake inputs.

Such a system could also monitor other aspects of the undercarriage todetect problems related to the wheel and brake. This might involvemonitoring for example the temperature of the wheel bearing, thetemperature of the tire or the tire pressure.

Looking at a simple and common scenario, if the heat pack is worn therewill be less material available to absorb the energy dissipated by anygiven brake application. This will result in a greater rise in heat packtemperature than would be seen in a new heat pack. The greater thedegree of wear, the greater will be the resulting rise in heat packtemperature.

Considering a different scenario, if all the drive tenons on a singlerotor disc are broken this will result in the loss of two frictionsurfaces. In such a case, when compared with a brake with all frictionsurfaces available, the same brake control system inputs of pilot brakedemand, brake fluid pressure, brake application time, wheel speed andanti-skid activity will result in a lower brake torque being generated,less rapid deceleration and a lower increase in temperature.Alternatively, if a deceleration regulating autobrake is in operation,it will act to regulate deceleration for a given pilot demand bycontrolling the brake fluid pressure. Hence, the main effect of thedrive tenons of a rotor disc becoming broken will be an increased brakefluid pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be well understood, it will now bedescribed by way of example only with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a simplified diagram of one embodiment of system of theinvention;

FIG. 2 is a simplified diagram of another embodiment of system of theinvention;

FIG. 3 is a graph relating to a first dynamometer test sequence on aparticular aircraft carbon disc brake with temperature T degrees C asthe ordinate and time S seconds as the abscissa and showing (A)temperature as represented by a signal from a temperature sensorincorporated in the brake and (B) the same signal after being filtered;

FIG. 4 is a graph similar to FIG. 3 but only showing (c) the filteredsignal and for a different dynamometer test sequence.

FIG. 5 is a main graph of amplitude M versus time T for the signal ofFIG. 4 after numeric processing using a computer, FIG. 5 also comprisesthree diagrams amplifying respective details of the main graph.

FIG. 6 is a simplified circuit diagram of a brake condition monitoringsystem.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The system shown in FIG. 1 is applied to one wheel 1 of an aircraft (notshown) having a carbon-carbon multi-disc brake assembly 2 with ahydraulic actuator mechanism 3. Mechanism 3 is driven through line 5 bya hydraulic system of a type containing an ASCU and known in the art. Abrake temperature sensing unit 4, typically a thermocouple, is locatedadjacent the assembly. To record brake usage, the signal from thethermocouple is input to unit 10 via an interface 11 to processor 12where the signal is processed by an algorithm in known manner to detectwhen a brake application has been made. The processor output is recordedin the Non-Volatile Memory (NVM) unit 13 from which information can bedownloaded from a suitable access port (not shown) inside the unit 10 oron an external surface of the unit.

In order for unit 10 to be able to function independent of other controlsystems on the aircraft there is provided within unit 10 battery means14 for providing power to the unit. During the majority of the unit'slife the aircraft will be stationary or in flight, therefore, in orderto preserve battery power, and hence extend unit life, a tilt switch 16and a motion sensor 15 are present. The tilt switch would break thepower line from the battery to processor when the undercarriage isretracted and the motion sensor will be used to send the processor intosleep mode during periods of inactivity.

Referring to FIG. 2, outputs from the thermocouple 4, brake pressuretransducer 6 and wheel speed transducer 7 are taken from an aircraftwheel, brake and brake actuation system (not shown) of a type shown inFIG. 1. These output signals are input to the processor 24 in unit 20via signal conditioning interfaces 21, 22 and 23. The signals areprocessed by algorithms to detect when a brake application has been madeand the type involved. The processor output is recorded in unit 25 fromwhich information can be downloaded from a suitable access port (notshown) inside the unit 20 or on an external surface of the unit. Recordsdownloaded from the unit will show not only the number of brakeapplications but also the type of brake application, for exampledistinguishing between taxi snubs and landings.

A “wake-up” call 26 is again incorporated to preserve the life of thebattery 27 and can incorporate functions such as a tilt switch and/ormotion sensor as described for the system of FIG. 1.

The systems of FIG. 1 and FIG. 2 represent stand-alone units added tothe aircraft to monitor the brake applications, but the processing ofthe signals to be detailed below can also be incorporated into existingbrake control units by modification of hardware and/or software.

In the systems described above a temperature signal at the BrakeTemperature Monitor Sensor (BTMS) is shown at A in FIG. 3 for three taxisnubs performed on a dynamometer for a carbon brake from a regional jetaircraft. Temperature rises TR1, TR2 and TR3 in the order of 2.5° C. areshown but noise resulting from interference by other equipment makes theshape of the trace difficult to see. The system therefore includes meansfor filtering, differentiation and amplification of the signal.

The signal B of FIG. 3 has been processed by a fourth order filter.Although the trace is now smooth the individual temperature rises causedby each brake application are not easily detected so the signal isprocessed further by differentiating twice and amplified. A suitablecomputer program performs the necessary numeric algorithm and makes adecision on whether or not a brake application has taken place, if so,the brake application can be recorded. FIG. 4 shows the output for afull dynamometer test sequence consisting of three taxi snubs, one fulllanding followed by three taxi snubs, a short rest period and thenanother three taxi snubs. FIG. 5 shows the same output after processingusing the algorithm. Peaks above a predefined amplitude in the FIG. 5output indicate brake applications. From FIG. 5 the peaks clearlyidentify all the individual brake applications of the dynamometer testprogram. This dynamometer test work has been found to read across todata taken in aircraft testing. It has been shown in testing with theprocessed temperature signal that a reliable indication of a brakeapplication can be detected even where temperature changes of less than1° C. are seen.

Analysis of the output is more suited to some aircraft than others,depending on the positioning of the BTMS in the brake. The optimumposition for temperature sensing will depend on the design of the brakein question. In some brakes the optimum position might be close to thecenter of the heat pack. Generally the closer the temperature sensor isto the optimum position in the brake the more sensitive will be thetemperature detection during a brake application. For example, thesensitivity for temperature measured at the center of a four rotor brakemight be several times greater than elsewhere within the brake.

The processed temperature data can be recorded on its own to give anindication of the number of brake applications using apparatus such asis represented in the diagram of FIG. 1, or combined with wheel speedand/or brake pressure to give a more detailed record of the type ofbrake application that has been made, i.e. taxi snub or landing usingapparatus as shown in FIG. 2.

The invention is not limited to the embodiment shown. The signals may bederived from and processed by components in existing brake controlunits. The temperature may be sensed or measured using a device otherthan a thermocouple.

The system shown in FIG. 6 incorporates an electronic brake managementcontroller 101 of a type known in the art to manage all aspects of brakecontrol including monitoring pilot braking demand and controlling theapplication of pressure to the brake in accordance with pilot demand anddetected skid activity. Pilot brake demand inputs to the controller areprovided by monitoring means 104. These inputs include but are notlimited to pedal deflection and pressure demand. The controller willalso monitor signals from sensors in the wheel 103 and brake 102including but not limited to wheel speed, temperature, pressure statorposition, brake torque, brake fluid pressure. Signals from sensors inother areas of the undercarriage such as, for example the tire and axlecould also be used to monitor the condition of a range of components andassemblies forming part of the aircraft landing gear. Also, informationsuch as aircraft weight could be inputted to the controller from one ormore other a/c systems (these are represented by block 107 in thedrawings).

The controller analyzes the signals relating to pilot demand and thebrake to evaluate a brake performance signature indicative of how thebrake is performing. This brake performance signature could be comparedagainst the signature for a heat pack in as new condition.Alternatively, over a period of time a record of a brake's performancecan be built up that will allow statistical analysis showing trends inthe brake performance signature and allow the controller to predict anexpected signature for a given brake application. Where deviations fromthe expected signature occur the controller would be able to identifypotential brake problems that might have caused the variation.

Problems identified could then be signaled to an on-board maintenancecomputer 105 capable of alerting the crew or ground maintenance staff.Alternatively, or additionally data from the controller could bedownloaded from a data port by ground staff during routine maintenanceor pre-flight inspection. Such a port 106 could also be accessed by thebrake supplier for downloading information about brake service,including number of brake applications and type of brake application.This service information could be used on its own or in combination withcondition monitoring data for brake life prediction and/or commercialpurposes.

Such a brake management controller could also manage the auto-brakingfunction of the braking system.

In the system of FIG. 6, the extent of heat pack wear is estimated bymonitoring pilot brake demand and signals from wheel speed, brake fluidpressure and brake heat pack temperature. For a given set of operatingconditions, for example, brake demand and speed, the controller comparesthe measured temperature rise with an expected temperature rise. Thedifference between these values gives an indication of heat pack wearwith a greater degree of wear resulting in a greater temperature rise.Additionally, the controller incorporates a threshold value oftemperature difference for any braking requirement, the threshold valuerepresenting the difference between the temperature expected for a newheat pack and a fully worn heat pack. As this threshold value oftemperature difference is approached, the flight crew or ground crew arealerted that the heat pack is approaching the wear limit. Alternatively,the controller or onboard maintenance computer could send a signal usingknown communications technology, such as for example via satellite link,to the aircraft operator's maintenance base or the brake supplier's baseso that maintenance action may be planned and replacement partsprovisioned. Such signals could be sent on a regular basis to allowexternal monitoring of brake condition or once only when the wearreaches a predetermined value to alert that maintenance and sparesprovisioning is required. The timing of such an alert signal could allowfor the lead-time for supply of the parts thereby minimizing stocklevels and hence reducing working capital of the brake supplier andaircraft operator.

The heat pack might lose mass for reasons other than wear, for example,by oxidation of carbon friction material or loss of a number of drivetenons. Such loss of mass will result in a larger increase intemperature in the brake performance signature than would be seen if thefault were not present.

Where the reduction of mass is caused by loss of a number of drives inthe heat pack, this would result in a step increase in the temperaturerise during a brake application when compared to the temperature risepredicted from statistical analysis of brake signature trends for anumber of stops over a period of time. The size of the step increase intemperature during brake applications would be greater the more driveswere removed from the discs in the heat pack.

Estimates of heat pack mass can also be made from X_(ps) and (delta)T(refer to Table 1). If these estimates of mass do not match this wouldsuggest some form of damage such a broken drives or oxidation.

A disc with all drives broken off is detected in the system of FIG. 6 bymonitoring signals representing brake torque, brake temperature and thebrake acoustic signature. If the drive tenons on a rotor disc or doublestator disc are broken this will result in the brake having two lessfriction surfaces when the brake is applied. For a given brake demand,brake pressure, duration of brake application and wheel speed there willbe a correspondingly lower torque generated because of the loss of thetwo friction faces and a resulting lower brake temperature than would beseen under the same brake application conditions with a heat pack whereall friction surfaces are operational. The number of ineffectivefriction surfaces in a brake will depend on the extent of damage to theheat pack. The deviation in brake torque and temperature from expectedvalues could be analyzed to determine how many friction faces wereineffective.

In comparison, under auto-braking conditions, if the drives on a discare broken the brake will be controlled to achieve a predetermined braketorque and the system will deliver an increased brake fluid pressure toachieve this required torque. Therefore, under auto-braking a pressurehigher than expected would indicate a disc with broken drive tenons. Thedeviation in brake pressure from that expected could be analyzed to givean indication of how many friction surfaces were no longer effective, soproviding an indication of the extent of damage.

In a brake with broken drive tenons on a disc, the acoustic signature ofthe brake during brake applications will be different from the acousticsignature of a brake with the same amount of wear and all friction facesworking effectively. The acoustic signature is detected by a microphone.The signal from the microphone is input to the brake managementcontroller for analysis to detect variations from the expectedsignature.

Other scenarios outlined in Table 1 could be detected and reported in asimilar way to those scenarios described above. The scenarios outlinedin Table 1 are to be considered as illustrative examples of brakeconditions that could be detected and not an exhaustive list.

References herein to brake odor, scent and olfactory sensing applies tothe process using appropriate transducers of detecting the presenceand/or level of certain gases or combinations thereof and/or of vapor orparticulates in and around the brake apparatus. TABLE 1 Expected Changein Signature For Constant Pressure For Autobrake Failure Modes Demand(deceleration) demand Cracked High T_(B) High T_(B) Brake Disc and/orand/or ΔAcoustic ΔAcoustic Broken Drive Low τ High P and Low T_(B)and/or ΔAcoustic Missing Large ΔX_(PS) Large ΔX_(PS) Brake Disc and andLow τ High P Residual Torque ΔT_(B) Δ_(B) and/or and/or Δτ Δ and and NoΔPedal/ΔX_(PS)/ΔP No ΔPedal/ΔX_(PS)/ΔP Excessive Low τ High P Oxidationand/or and High T_(B) High T_(B) Excessive Variation in T_(B) Variationin T_(B) Spline Friction across brake across brake Excessive ΔOlfactoryΔOlfactory Contamination Cracked ΔAcoustic ΔAcoustic Torque Tube TyreFuse Low P_(Tyre) Low P_(Tyre) Plug Leakage Wheel Bearing HighT_(Bearing) High T_(Bearing) Fatigue FailureNote:Low/High refers to lower/higher than expectedPossible sensor inputs:P₈

Brake Fluid Pressureω

Wheel Speedτ

Brake TorqueX_(Pedal)

Pedal Deflectiont

TimeAcoustic

Brake Acoustic SignatureT_(B)

Brake Temperature, measured at various positions through brakeX_(PS)

Pressure Stator Positionα

AccelerationOlfactory

ScentT_(Bearing)

Wheel bearing TemperatureT_(Tyre)

Tyre TemperatureP_(Tyre)

Tyre PressureΔ

Change in

1. An aircraft brake monitoring system for monitoring the usage ofaircraft brake members having facing friction surfaces, the systemcomprising means for detecting each actuation of the brake members andmeans for making a separate record of each said actuation in which thereis relative movement of the facing friction surfaces which causes wear,and from that separate record determining brake usage.
 2. A systemaccording to claim 1, including means for generating a signal accordingto an increase in temperature of the brake members on actuation thereofand means for distinguishing between non-wear generating actuationswhich cause a said increase below a threshold value and wear generatingactuations which cause a said increase above the threshold value.
 3. Asystem according to claim 2, including means for filtering anddifferentiating the signals generated by said means for generating asignal.
 4. A system according to claim 3, wherein the means forfiltering and differentiating is arranged to differentiate the signaltwice.
 5. A system according to claim 1, comprising a stand alone unitand a dedicated battery therefor.
 6. A system according to claim 5,including means for disabling the battery.
 7. A system according toclaim 6, wherein a tilt switch and/or motion sensor are present as thedisabling means.
 8. A method of monitoring the usage of aircraft brakemembers having facing friction surfaces, the method comprising:detecting each actuation of the brake members; making a separate recordof each actuation in which there is relative movement of the facingfriction surfaces which causes wear; and determining brake usage fromthat record.
 9. A method according to claim 8, including the steps of:detecting a change in temperature of the brake members on actuationthereof; generating signals according to the detected changes; andidentifying from said signals actuations of the brake members whichcause a change in temperature that is an increase above a pre-selectedthreshold value.
 10. A method according to claim 9, wherein theactuations which cause a change in temperature that is above thepre-selected value are identified as actuations in which there isrelative movement of the facing friction surfaces that causes wear. 11.A method according to claim 10, comprising differentiating said signalsbefore comparing said signals with said pre-selected threshold value.12. A method according to claim 11, comprising twice differentiatingsaid signals before comparing said signals with said pre-selectedthreshold value.
 13. A method according to claim 8, in which eachactuation of the brake members that is judged not to cause wear is notrecorded.
 14. A method according to claim 8, wherein the records ofactuation of the brake members are processed to generate expected brakeoutput values for respective brake inputs that cause the actuations. 15.A method according to claim 14, wherein the records of actuationcomprise actual brake output values and determining brake usagecomprises comparing an actual brake output value with the expected brakeoutput for the respective brake input to determine a brake wearcondition.
 16. A method according to claim 15, comprising initiating abrake maintenance action based on a determined brake wear condition. 17.A method according to claim 14, wherein the records of actuationcomprise actual brake output values and determining brake usagecomprises comparing an actual brake output value with the expected brakeoutput for the respective brake input to determine a brake faultcondition.
 18. A method according to claim 17, comprising initiating abrake maintenance action based on a determined brake fault condition.19. Aircraft brake monitoring apparatus for monitoring usage of aircraftbrakes that comprise carbon-carbon multi-discs, said apparatuscomprising: at least one sensor for sensing a brake output parameter andproviding signals indicative of values of the sensed brake outputparameter; a processor for processing said signals using at least onealgorithm to determine when a wear generating application of the brakeshas been made; and a store in which a record of each wear generatingapplication is stored.
 20. Apparatus according to claim 19, wherein saidsensed brake output parameter is temperature and said processor onlydetermines a wear-generating brake application when a temperature changeabove a predetermined threshold value is detected.
 21. Apparatusaccording to claim 20, comprising a differentiator for differentiatingsaid signals indicative of temperature at least once, saiddifferentiator being arranged for supplying differentiated said signalsto said processor.
 22. Apparatus according to claim 19, arranged suchthat when said processor determines that a brake application is not awear-generating application, a record of the non-wear generatingapplication is not made.
 23. Apparatus according to claim 19, operableto generate expected brake output parameter values based on the sensedbrake output parameter values.
 24. Apparatus according to claim 23,comprising a comparator for comparing expected brake output parametervalues with said sensed brake output parameter values to determine atleast one condition of the aircraft brake.
 25. Apparatus according toclaim 24, wherein said at least one condition is a wear condition. 26.Apparatus according to claim 24, wherein said at least one condition isa fault condition.
 27. Apparatus according to claim 24, operable toinstigate a maintenance action based on said at least one condition. 28.An aircraft comprising an aircraft brake monitoring system according toclaim
 1. 29. An aircraft comprising an aircraft brake monitoringapparatus according to claim 1.